Electric induction furnace



APril 6, 1937- J. R. WYATT,k I 2,076,216

ELECTRIC INDUCTION FURNCE Filed March 1o, 19:55 2 sheets-sheet 1 J. R.WYATT ELECTRIC INDUCTION FURNACE Filed March l0, 1955 2 Sheets-Sheet 2April 6, 1'937.

Patented Apr. 6, 1937 PATENT oFFi'cE 2,076,216 ELECTRICrNnUo'rroNrUnNAoE James it. Wyatt, Camden, N, J., assignor to AjaxElectric Furnace Corporation, Philadelphia, Pa., a corporation ofPennsylvania Application March 10, 1933, Serial No. 660,202

el claims.

My invention relates to .submerged channel electric induction furnaces.

A purpose of my -invention .is to improve the stirring in a submergedchannel electric induction furnace.

A further purpose is to eliminate some of the wear upon the refractorywalls of the submerged channel of an electric induction furnace.

A further purpose is to reduce superheating in the submerged channel ofan electric induction furnace. p

A further purpose is to vremove the magnetic damming effect from anelectric induction furnace submerged channel.

A further purpose is to start primary-on-secondary stirring in the'submerged channel of an electric induction furnace at the same point atwhich secondary-on-secondary stirring is-initiated. I

A further purpose is to concentrate iluxat the bend of a submergedchannel anglehaving the A point of the angle directed away from anyelectric induction furnace pool.

In a submerged channel electric induction furnace having a V-shapedchannel with the point of the V directed from the pool of the furnace, afurther purpose is to place the core of a coretype transformer aroundthe bend of the V and to locate a coil surrounding the core between thebranches of the V.

Further purposes appear in the specification and in the claims.

My invention relatesto the methods involved,

and the apparatus used to carry out the methods.

In the drawings I have illustrated the furnace of my inventiondiagrammatically, eliminating purely structural features, such as theouter furnace supports and' tilting mechanism, and the numerousaccessories used with every furnace.

I have chosen to illustrate two only of the main forms of my invention,selecting forms chiey for the sake of clear explanation of theprinciples -involved and convenient exemplication of the r main featuresofiny invention.

Figure 1 is a top plan view of a furnace having a depending channel,made in accordance with my invention'.

Figure 2 is a central vertical section of Figure 1, taken on the line 22.

Figure 2a is a fragmentary view corresponding tol Figure 2, but showinga modification;

Flgure 3 is a fragmentary section of Figure 2 on the line 3-4. y

Figure 4 is a fragmentary section of Figure 2- on the line I-L Figure 4ais a view corresponding to Figure 4 and illustrating a modified channelcross section.

Figure 4b is a view generally similar to Figure 4, but with a differentchannel cross section.

Figure 5 is a side elevation of a somewhat different furnaceembodying myinvention.

Figure 6 is a section of Figure 5 upon the line 6 6. f Figure 7 is afragmentary section of Figure 6, taken upon the line 1-1. y

Figure 7a is a view similar to Figure 7, showing a different channelcross section.

Figure 7b is a view corresponding to Figure '7, and illustrating anothervariation in channel cross section.

Figure 8 is a fragmentary diagrammatic view of a' prior art furnace.

Figure 9 is a fragmentary diagrammatic view of a furnace of myinvention. f

In the drawings, like numerals refer to like parts.

My invention relates particularly to submerged channel electricinduction furnaces in which heat is developed by induction in a moltenconductor, and the heat is conveyed,j primarily by ,circulation of themolten conductor, to a pool of -molten charge, to which solid charge maybe added for melting if desired.

My invention is particularly applicable to submerged channel electricinduction furnaces of Patent No. 1,201,671,

the type shown in my U. S.

may also be applied Figures i to 6, inclusive, but

to other submerged channel electric induction My electricinductioncfurnaces are ordinarily used to melt metals and alloys and, toheat and superheat metals and alloys which have been melted, althoughany charge which is electrically conducting when molten 'and which canbe vTheated in much the same way as a metal or alloy,

may be used in my furnaces,

l Circulation is of great importance in -submerged channel electricinduction furnaces, not only because it is relied upon to convey heatedcharge to the pool of molten charge, but because, without adequate andproperly controlled circulation, the charge in the molten .conductorwill reach an abnormally high temperature at which attack upon therefractory lining of the channel will be more rapid, at whichvaporization of charge in the channel may occur and at which otherundesirable effects of overheating may be observed. L.

In the drawings, two m-ain types of submerged channel electric inductionfurnaces are shown.l The type illustrated in Figures 1 to 4b inclusive,commonly known in the art as the 'Ajax-Wyatt type, has a dependingchannel or a channel lo- 5 cated vertically below the pool of moltencharge (see my U. S. Patent No. 1,201,671, Figures l to 6, inclusive).The type illustratedl in Figures 5 to 7b inclusive has the submergedchannel placed at one side of the pool (see my U. S. Patent No. l1,201,671, Figures 7 to 10a, inclusiyle).

Referring rst to the form of Figures 1 to 4b,

inclusive, the bulk of the charge, whether molten Ior partially solidand partially molten, forms a pool 30 contained within a holder orcrucible 3l l comprising suitable refractory material. Charge may beremoved from the crucible, as for example by tilting the furnace aroundtrunnions 32 and 33 to pour from a spout 3l.

While the holder or crucible has been shown as a cylindrical relativelydeep vessel, filled with charge to a suitable depth, as for example, upto a level 35, it will be understood that any proper shape of cruciblemay be used, as best suited to the particular case, and the depth andcontour of the crucible may be adjusted accordingly.

The charge is heated by a submerged channel 36 having branches 3l and 38meeting at 39 in an angle whose point is directed away from the pool 30.The channel is markedly diverging at its ends G0 and di, and desirablyhas a groove d2 joining the two branches at the ends.`

Both of the ends lill and #I of the submerged channel communicate withthe pool, so that molten charge from the pool may freely enter thechannel, and likewise molten charge from the channel may readily minglewith the pool.

The channel is effectively a V, whose bend is located at d3. l

The angle N oi the V, which is the angle be- 40 tween the adjacentstraight portions of the branches of the channel, may vary from theangle shown in Figure 2. For example, in Figure 2a the angle 44 of the Vis an obtuse angle rather than an acute angle as shown in Figure 2, and45 any type of angle between an extremely obtuse angle and a very acuteangle may be used, provided the angle point faces away from or isdirected away from the pool, and does not reach 180 or greater forreasons later explained.

The submerged channel 35 is formed in a chan- .nel block l5 consistingof suitable refractory material such as magnesia, chrome, etc., anddesirably is cemented to the Crucible 3l at 46.

The transformer core 4l is preferably rectangu- 55 lar, and is ofcore-type as distinguished from shell-type, and comprises a side 49passing through the coil 48, a side Ell parallel to the side i9 andlocated below and close to the point of meeting of the two branches diuthe submerged channel and sides 5i and 52 respectively parallel to one.another and transverse to the sides 49 and 50.

The transformer core 4l will of course be made of laminated sheets oftransformer irn, which are assembled by overlapping individual sheets atpoints of joining as in conventional transformerpractice. No attempt hasbeen made to indicate where individual laminated plates end and othersbegin in making up the core.

The coil 48 suitably comprises one layer ci turns wrapped around theside I9 of the transformer core, and located in an opening 53 throughthe refractory of the channel block 45. Heat and electrical insulationof the coil have been omitted. The walls of the channel curve at 54preferably around the same axis of curvature as that of the coil, andthe straight portions 55 and 58 of the branches 31 and 38 of thesubmerged channel are preferably tangential at 5l to the .curved portion5l.

The present invention applies to submerged channel furnaces havingangles in the channels whose points are directed away from the pool,whatever the cross sectional contour of the submerged channel and thecontour is therefore not specifically claimed in this application.However I have discovered and will elsewhere claim that a channel havinga circular contour 53 as shown in Figure 4 is of special advantage inall angle type submerged channel furnaces, whatever the form orpositionof the transformer. The edgepresented contour 59 of Figure 4a might alsobe used and somewhat less desirably the fiat-presented contour of Figure4b could be employed. It will be understood that these are examplesmerely, and that considerable variation can be made in the type ofcontour used.

The coil 48 is protected from the molten charge yby the refractory wallsof the channel, and may be cooled if desired by any suitable means, suchas a blast of air. Likewise, the transformer core Il is protected by therefractory material, and may be artificially. cooled if this be deemednecessary. To avoid transfer of heat from the bend of the channel at 39to the side 50 of the transformer core, a layer of heat insulatingmaterial, such as asbestos board is located at 8| between the refractoryand the core material.

It will be evident at once that the form of Figures 5 to 7b, inclusive,is generally similar to that of Figures 1 to 4b, inclusive, except thatin Figures 5 to 7b, inclusive, the submerged channel extends laterallyfrom the pool.

Without repeating, in the description of the form of Figures 5 to 7b,inclusive, the parts already described in relation to Figures l to 4b,inclusive, it will be evident that the channel 38 as seen in Figure 6need not be of exactly the elusive, are, however, the same as those ofFigures 1 to 4b, inclusive. In both cases the subbranches of the channelmay be varied, and the contour of channel cross section may be altered.`In.Figures 7, 'la and 7b, the same three channel cross sections areshown as are illustrated in Figures 4, 4a and 4b.

In the prior art, the generalpracti'ce has been to construct a submergedchannel electric induction furnace as illustrated in Figure8, with' thecoil between the branches of the channel surroundin'g the middle leg ofa shell-type transformer core, whose youter legs are each outside thechannel.

The submerged channel is heated by electric amano current induced in itfrom the primary coil 4l.V This induced current ilows through thechannel and through' the pool from one channel end to another.

In a submerged channel having an angle whose point is directed away fromthe pool, a stirring tendency originates at the point 39 of meeting ofthe branches. due tothe action of the electric current in one. branch ofthe channel upon the electric current in the other branch. This tendencyis referred to by me as secondary-on-secondary stirring, and is aneffect of the repulsion of. one conductor upon another. Due to thesecondary-on-secondary stirring, there is a tendency to cause moltenmetal to iiow upwardly from the point 39 along the outside of thechannel in each branch toward the pool as indicated by the arrows 64,and to permit molten metal to flow by gravity down the inside of thechannel zo from the pool as indicated by the arrows 05, to

replace the upwardly flowing molten metal.

The secondary-on-secondary repulsion stirring isa very important aspectof any submerged channel induction furnace having an angle whose pointis directed away'from the charge. .and is due to the presence of theangle. If the channel lacked the angle M and were circular as viewed inthe plane of the length of the channel .(that is, in the plane of thepaper in views such as Figures 2, 2a, 6 or 8). the repulsion forceswould be nearly balanced, completely balanced if there were a completecircle of uniform cross section and secondary-on-secondary repulsionstirring could be ignored. It is by virtue of the V or the angle havingits point directed away from the pool that secondary-on-sec'ondaryrepulsion is so greatly accentuated. This was shown and discussed inmy'U. S. Patent No. 1,201,671. n

In addition to secondary-on-secondary stirring, there isprimary-on-secondary'stirring in an electric induction furnace of thetype under discussion. Primary-on-secondary stirring tends to cause iiowaway from the point of concentra- 45 tion of the leakage field. In theprior art, where the shell-type transformer was used, the 1eak` agefield in the channel was most concentrated at some points 66 between thelegs of the trans- A former core. This results in a tendency ofthemolten charge to flow in both directions (in and out) through thechannel away from the points B6 of high leakage field intensity.

The primary and secondary`currents are both strong and opposite (180apart) in direction. Their fields, one clockwise and the othercounterclockwise about its conductor, will therefore have the samedirection at some points 61 between them and immediately inside thechannel. The` reaction of one field upon the other will tend to forcethe molten metal charge within the channel to follow the outside of thevchannel in moving away from the points of high field intensity 66 whichis intensified under the iron core. Asa result, there 4is pressurecausing a tendency to flow in both directions in each branch of thechannel, down and up the outside as indicated by the arrows B8 and 89,and forany. flow which takes` place, a resulting gravity flow into thiszone as shown by the arrows 10 and 1I, to take the place of the moltenmetal removed. The force indicated by thearrow I8 directly helps to movemolten metal toward the pool, but the force represented by the arrow 88tends to move molten metal toward the point 39 where 75 the branches ofthe channel meet. This tendency is in direct opposition to the upwardflow at the outside of the channel due to secondaryon-secondaryrepulsion indicated by the arrows 64, and would prevent upward ilow wereit not for the fact that the secondary-on-secondary stirring (arrow 64)is more powerful than the primary on secondary downwardly stirringpressure (arrow B8).

A s a result of the above, some of the chargeflows upwardly as indicatedby the arrow 12, overcoming the tendency to how downward indicated bythe arrow il. while another part of the charge is turned back toward thepoint i as indicated by the arrow 13. Likewise some of the downwardlyflowing charge indicated by the arrow 6l is returned upwardly asindicated by the arrow 14.

While the theory above cannot be verined prac- -tically in its entiretyit seems to me to be well founded and is confirmed in part, at least bythe fact that excessive lateral erosion takes place in the channel atabout the place where the eddy flow arrows 13 and 14 appear.

Pinch effect flow, due to the tendency of current in different parts ofthe same-molten conductor to constrict the conductor and to cause moltenmetal to flow upwardly/along the middle of the channel has beenconsidered in the above A disc'ussion, but has not been discussed beforenor further than is herein explained for the reason that the eliminationof counter-pressures along the outer walls' of the channel, provided bymy invention herein, is highly beneficial whether pinch enact/"be weakor strong. As a rough analogy, pinch effect flow may be compared to thetype of flow produced in a flexible hose when the walls are uniformlyconstricted from the outside. Pinch effect does not assist circulationexcept where there is a change in cross section. Since whatever ilowthere may be, whether strong or weak, merges with the flow produced bymy invention herein, my invention is beneficial whatever the pinch now.

From another standpoint also pinch effect dis-J cussion herein can beeliminated because pinch effectris a function of tube or channel designandthe tube can be designed to take care of the pinch eifect. Pincheffect. is not directly affected v by transformer design or position.

FromFigure 8 it will be clear vthat the primaryon-secondary pressure ofthe prior art form hav-V ing the shell type transformer tends to causecirthe molteny metal gets up to the medial line of the transformer thatthe chief effect of the pri' mary-on-secondary pressure above the medialline'will be to cause local circulation from this medial line up to thepool and back again. In any event, the lprimary-on-secondary pressureabove themedial line can be of little benefit in assisting circulationwithin the channel below the l medial line. vAt most it will makecirculation a little easier by clearing metal out of the way'along theouter wail of the channel from a point at. which circulation has alreadybegun to be easierA to effect by reason of the flaring oi' the channel.

In other words, whatever assistance primary-onsecondary` pressure abovethe medial transformer line offers in clearing metal out ahead o3 thesecondary-on-secondary flow is not effective until 5 a point in thechannel is reached at which the fluid resistance to upward molten metalflow along the outer channel wall has been reduced and is beingprogressively lowered by enlargement of the channel.

l For the reasons above, beneficial effect of primary-on-secondarypressure upon the molten metal above the medial transformer line is muchless than the injurious effect of the counter pres- 1 siure in that partof the channel below the medial 5lne.

This is true even without considering the eddy currents produced withinthe channel as by flow shown at i3 and 14 and becomes more pronounced-when the objectionable washing effect of the counter fiow isconsidered. V

It will be evident therefore that the damming effect of the oppositionto upward current now produced by primary-on-secondary stirring in itsentirety is a direct hindrance to secondary-onlv secondary stirring. Inother words, the shell type transformer produces a magnetic dam which,

reduces and alters the character of the secondary-on-secondary stirringWithin the submerged channel and which damages the. channel not only 3because of the reduction in the speed of clearing molten metal, causingunnecessarily high temperature within the channel, but because of theerosion of the channel walls weakened against erosion by the highertemperature.

'5" The magnetic damming action of the shelltype transformer has otherundesirable effects in that cutting down the stirring in the channelmakes the circulation of the molten metal more sluggish as it dischargesinto the pool reducing 40 the mixing effect and resulting in anundesirable dillerence in temperature in different parts of the poo Itwill be evident that the temperature differenr tial between the pool andthe channel will be 4" maintained whatever the temperature of the pooland cannot be equalized by merely operating the furnace longer toincrease the pool temperature since molten metal owing' down from thepool at the higher temperature will again be increased in temperature byreason of the unnecessarily reduced flow of metal in the channel.

A further undesirable feature of the magneticY damming action is that,due to the high temperature differential between the submerged channeland the pool, molten metal in the channel is likely to be vaporized,particularly where a high energy input into the furnace is employed.Vaporization on account of magnetic damming gives rise to the phenomenonof kicking, occurring in furnaces operating on brass and otherzinc-containing metal. The kicking is due to vaporisaton of zinc, whichbreaks the electrical circuit through the submerged channel and causesmomentary cessation of heating. When the vaporized zinc .has` passed outof the channel, molten metal flows in 'to fill the space which itoccupied, producing a noise known as a bump and causing coincident shockand stress to the channel walls. with corresponding weakening of theWalls 0 and in some cases with strain or even rupture of the walls.

I have discovered that the difficulties present in the use of theshell-type construction acrosschannels meeting .in a V whose point isdirected away from the pool. as shown in Figure 8, may

be avoided by using a core-type transformer located about the point ofmeeting of the branches of the submerged channel. For such aconstruction, circulation lines as they appear to operate are shown inFigure 9, with upward flow indicated by the arrows 64', and downwardflow indicated by the arrows 65'. The upward flow. (arrows 64') ispartly primary-on-secondary and partly' secondary-on-secondary stirring.

My construction gives a maximum advantage for the secondary-on-secondarystirring effect already described, both through concentration ofelectromagnetic effect at the V (due to the transformer position linkingthe V) and because of the elimination of the counter force representedin Figure 8 by arrow 68 due to primary-on-secondary force in the priorart form.

Not only is the secondary-on-secondary effect increased therefore andthe magnetic darn, due to primary-on-secondary effect in the Figure 8form, eliminated, but the primary-on-secondary pressure which previouslyconstituted the dam is applied to assist instead of opposing .thesecondary-on-secondary pressure movement.

In the present invention, primary-on-secondary stirring still tends tosend the charge in both directions along the channel from the point ofconcentration of flux, but this point is now the point 39 at which thebranches of the channel meet, the same point at which thesecondary-onsecondary forces are concentrated and from which theyspring, and both stirring effects combine to send charge up the outsideof each branch, no longer bucking one another.

In addition to the great advantage of applying this primary-on-secondarypressure beneficially, changing a bucking liability to an assisting"asset to clear the channel quickly, reduce the temperature in thechannel and correspondingly to reduce the temperature differentialbetween the channel and the pool, I secure a decided beneiit also ineliminating molten metaleddy currents such as are shown at 13, 'M

The use of core-type transformers about the points of angles insubmerged channels has been attempted in which the point of the angle ofthe channel is directed toward the pool.

The attempt to use the core-type transformer about re-entrant angles asabove has not produced the advantage nor the ilow relations of myinvention. The reason for this is that though the primary-on-secondaryrepulsion produced tends to cause flow up the inside of the outer wallof the channel, with gravity return flow down the inside of thechannel-as in the present inventionthe secondary-on-secondary tendencyto flow is out along the inner surfaces of the inner wall of the channelpassage, which are the surfaces farthest from each other at the angle.This causes secondary-on-secondary flow along the inner channel walls atthe angle directly opposing gravity retu'rn ilow from theprimary-on-secondary circulation. Moreover, normalreturn flow for thissecondary-on-secondary inside channel circulation is down along theinner face of the outside wall of the channel, directly in line with andopposing the primary-on-secondary flow.

It will be evident that the re-entrant angle form concentrates the fluxfrom the core-type of transformer disadvantageously at the angle insteadof .advantageously and loses all `of the adg vantages of my invention.

By explaining the theory upon which my invention is believed to operate,I do not wish to limit myself to this theory nor to make thecorrectness' oi' the theory essential to the protection afforded myinvention. Asidevfrom the theory, I find that the practical resultsobtained by my invention are highly desirable, in quicker and moreefficient heating, better stirring and much longerlife` ofthe'refractory in the submerged channel. 'I'he results of the tests madeupon my invention are remarkable and convince me of the commercialfeasibility of the furnace of my invention.' not only for alloys ofvlower melting point, including brass relatively high in zinc, such asred brass, copper, but also for iron and steel.

It will be evident that both of the moving forces used(primary-on-secondary and secondary-on-secondary) are motor effects.

In view of my invention and disclosure variations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled in the art, to obtain all or part of the benefits of myinvention without copying the structure shown, and I, therefore, claimall such in so far as they fall within the reasonable vspirit and scopeof my invention.

sole energizing means for the magnetic circuit,.

located between the said converging branches and effective to set uplines of magnetic force in the magnetic circuit having a maximum at theangle.

2. In an jelectric induction furnace, walls forming a crucible for'acharge, walls forming a V- shaped single-conduit channel filled withmolten charge when the furnace is in operation, communicating with thecrucible and having the point of the V directed away from the crucible,a closed magnetic circuit individual to the channel surrounding thepoint of the V and passing through the spacing between the channel wallsand a primary winding upon the portion of the closed magnetic circuitbetween the channel walls, the transformer being free from winding inproximity to the V.

3. In an electric induction furnace, a crucible adapted to hold a moltenmetal charge. walls forming a single-conduit submerged channel dependingfrom the crucible, having two branches, each communicating with thecrucible at its upper end, converging one with respect to the otherbranch along a straight portion and meeting the other branch at itslower end in an angle whose point is directed downwardly and atransformer core passing around and linking the angle, having its soleexciting coil between the channels and part of said core outside of butclose to the angle for concentrating flux at the angle in excess of thatin the channel branches close to the crucible, there being but onechannel per transformer. l

4. In an electric induction furnace, a crucible adapted to hold acharge,'walls forming a submerged channel depending from the crucible,communicating at its upper ends with the crucible and having a V-bendwhose angle point is directed away from the crucible, a closedrectangular transformer core surrounding the V- bend, having a firstside extending transversely of the plane of the channel above theV-bend, a second side parallel to the first below the V- bend, and thirdand fourth sides joining the ends of the first two sides, there beingbut one channel conduit within th-e transformer core, and electricallyenergized means including a coil surrounding said first side andcomprising the sole energization of the core to set up lines of magneticforce in the magnetic circuit having a maximum at the angle.

5. In an electric induction furnace, a crucible, walls forming asingle-conduit submerged channel extending laterally from the crucible,communicating at its ends with the crucible and having an angle whosepoint is directed away from the cruciblel and transformer means forconcentrating flux at the angle including a core linking the channelwith one leg adjacent the angle and a transformer coil within the anglewhich coil aords the Sole energization for the transformer.

6. In an electric induction furnace, a crucible,

walls forming a V-shaped single-conduit channel nearer to one-side ofthe crucible pool than to the other side, communicating at its ends withthe lower part of the crucible and having the point of the angleextending away from the crucible and a transformer having a rectangularcore surrounding thebend of the V and having its soie excitation from acoil surrounding one leg of the core and inside the V.

JAMES R. WYA'I'I.

